Marconi, which was worth #35 billion last year after its shares reached a high of #12.50, was today worth just under #1 billion.

The fall came on a tough day for the rest of the London market, with the FTSE 100 Index trading nearly 100 points lower by mid-morning.

Alex Scott, fund manager at Barclays Stockbrokers, said there appeared no end to the company's problems in the City: "It's difficult to see how Marconi can trade its way out of this hole.

"We have a price target of 30p, although I wouldn't be surprised to see them lower than that."

On Tuesday, unions described Marconi as "stumbling from crisis to crisis" after chief executive Lord Simpson and chairman Sir Roger Hurn quit and the firm said it would cut a further 2,000 staff - bringing job cuts to 10,000.

Management of the company have come in for a barrage of criticism following Marconi's disastrous performance and the City claimed a scalp earlier this year when John Mayo, the deputy chief executive, quit.

The shake-up follows Marconi's dramatic announcement two months ago when a profits warning wiped #4 billion off the value of the group.